Plugin error; Trying to parent custom frames

Hey there! So I am trying to make a more efficient version of @Stelrex’s roundify plugin. I am making it a dockable studio widget, and I am using [this github repo from roblox] (GitHub - Roblox/StudioWidgets). I keep getting attempt to call a nil value error when trying to parent a custom scaling frame to the widget. My code is below.

local toolbar = plugin:CreateToolbar("UI Elements")
local button = toolbar:CreateButton("Roundify", "Make UI look cleaner with UICorners!","rbxassetid://6024626465")

local LabeledTextInput = require(script.Parent.LabeledTextInput)
local CollapsibleTitledSection = require(script.Parent.CollapsibleTitledSection)
local LabeledCheckbox = require(script.Parent.LabeledCheckbox)
local VerticalScrollingFrame = require(script.Parent.VerticalScrollingFrame)
local VerticallyScalingListFrame = require(script.Parent.VerticallyScalingListFrame)
local GuiUtilitiesService = require(script.Parent.GuiUtilities)

local widgetInfo =
	Enum.InitialDockState.Right,  -- Widget will be initialized in floating panel
	false,   -- Widget will be initially enabled
	false,  -- Don't override the previous enabled state
	200,    -- Default width of the floating window
	300,    -- Default height of the floating window
	150,    -- Minimum width of the floating window
	150     -- Minimum height of the floating window

local widget = plugin:CreateDockWidgetPluginGui("Roundify Gui", widgetInfo)
widget.Title = "Roundify a Gui!"

local ScrollFrame =

local ScalingFrame =

local collapse =
	".button", -- name suffix of the gui object
	"Preferences", -- the text displayed beside the collapsible arrow
	true, -- have the content frame auto-update its size?
	true, -- minimizable?
	false -- minimized by default?

local input =
	"Input", -- name suffix of gui object
	"Intensity", -- title text of the multi choice
	"input a number!" -- default value

input:GetFrame().Parent = collapse:GetContentsFrame()


ScalingFrame:GetFrame().Parent = ScrollFrame:GetContentFrame()
ScrollFrame:GetSectionFrame().Parent = widget

	widget.Enabled = not widget.Enabled